[Dnsmasq-discuss] DHCPv6 Server not respecting lease time setting

[Simon Kelley]

On 31/07/13 23:06, Jonathan Fabian wrote:
> Hi,
>
> I'm seeing some strange behavior between my mac and dnsmasq (running on
> arch linux arm) when getting assigned an IPv6 address. Specifically, I
> have the DHCPv6 set to give out a 12 hour lease
> time: dhcp-range=a:b:c::1, a:b:c::ff, 64, 12h, but it will only give the
> mac a 2 min lease time (as a side note, I have also tried setting a dhcp
> host option specifically for macs duid and it ignores those lease time
> values as well). The lease time setting works fine with the windows
> machines on the same network.
>
> Looking at the network packets, I see the mac solicit the dhcp server,
> the dhcp server replies with an advertisement message offering an ip
> address with a valid and preferred lifetime of 43200, then the mac
> replies with a request for the advertised ip address with the valid and
> preferred lifetimes set to 0 (which looking at rfc3315 should be treated
> as no preference), dnsmasq then sends back a reply with the address but
> the valid and preferred lifetimes only set to 120 (the min time allowed)!
>
> The only difference I can see with the windows machines is that when a
> windows machine sends the request message they copy the preferred and
> valid lifetimes of 43200 from the advertise message.
>
> Maybe I'm wrong, but it seems that dnsmasq should always be ignoring the
> 0 when sent, and only treating the valid and preferred lifetimes from
> the client as a request at best. It seems, however, to be treating them
> in a manner that overrides the explicitly configured setting in its
> config files. Can anyone shed some light on this behavior?
>

Your analysis of the problem is beautifully clear, and captures the 
problem well. Sadly the actual code, on inspection, is really rather 
confused. For instance it uses the preferred lifetime field in IAADDR 
options from clients, but ignores the valid lifetime field.

I'll try and make time over the next couple of days to work through the 
whole tangle and try and sort it out.

Cheers,

Simon.